Toxic Plants

Horse chestnut: Lookalike of Sweet Chestnut and Chinquapin

With their spiked, green cases and glossy seeds, horse chestnuts (Aesculus hippocastanum) have become a telltale sign that Autumn is approaching. Common across Europe, and found within parkland across the US, these striking trees can be hazardous to foragers looking for tasty, edible sweet chestnuts or chinquapin seeds.

Often referred to as ‘conkers’, horse chestnut seeds are occasionally mistaken for sweet chestnut seeds. However, unlike their edible counterpart, horse chestnut seeds are toxic. There have been several instances across the World where naive foragers or children have accidentally consumed horse chestnut seeds, and become very ill as a result.

2 fruits on Aesculus hippocastanum (Horse-chestnut) | Photo by Jan Ainali on Wikimedia Commons

What are the active compounds in Horse Chestnut?

Horse chestnut plant parts contain a toxin known as aesculin. It’s a glucoside that can cause nausea, convulsions, and diarrhea. If a high dosage is consumed, particularly in young children, it can be fatal.

A number of toxic glycosides can also be found in horse chestnut trees, including saponins. These compounds protect plants from bacterial and fungal infection, and some saponins can irritate the digestive and respiratory tract. Saponins can also be found in the incredibly toxic pokeweed and manchineel plants.

Horse Chestnut poisoning symptoms

After ingesting seeds, raw or accidentally cooked, symptoms of horse chestnut poisoning include nausea, vomiting, diarrhea, throat irritation, convulsions, coordination issues, and even paralysis. In high doses, horse chestnut poisoning could also be fatal.

Horse chestnut ‘conkers’ in Germany | Photo by stanze on Wikimedia Commons

What is the medicinal potential of Horse Chestnut?

One of the saponins found in horse chestnuts has been identified and used in pharmacology. The saponin, aescin, has been used to successfully treat chronic venous insufficiency (CVI). Further study is needed, however, and home remedies are not recommended.

Cultural symbolism of Horse Chestnut

Horse chestnuts have several cultural uses within the UK. A children’s game known as ‘conkers’ has been popular for over two centuries. A hole is drilled in the hard seed and threaded with a shoelace that’s knotted at one end. Two opponents then take turns to hit each other’s conker with the other. The winner is whoever can break the other conker first.

A horse chestnut with a hole bored ready to be threaded onto a string for a game of conkers. | Photo by XCalPab on Wikimedia Commons

An ‘old wives tale’ in the UK states that putting a horse chestnut seed in corners within a house will repel spiders. Although there is currently little evidence to prove this.

In Germany, the trees were planted near breweries to shade lager and beer with their dense canopies. Today they are still widely associated with beer gardens.

Leaves and trunk of Horse chestnut. | Photo by Alvesgaspar on Wikimedia Commons

The horse chestnut is also one of several symbols of Ukraine’s capital city, Kyiv. The distinctive leaf of the horse chestnut, with its 5-7 leaflets, once featured on the city’s coat of arms and other cultural references like old coins and songs.

According to the IUCN horse chestnut trees are now considered vulnerable. Like the decimated American sweet chestnut tree, they are vulnerable to a number of bacterial and fungal infections.

What does Horse Chestnut look like?

Mature horse chestnut trees can grow up to 35+ meters. The trunk is typically grey, and scaly, and the canopy is a dense mass of bright green leaves. The leaves themselves are quite distinctive with palmate leaflets that are arranged around a central stem. The flowers form a clustered pyramid of pink to white flowers.

Horse chestnut flowers | Photo by Frettie by Wikimedia Commons

The spiked green seed casing and red/brown, glossy seeds have similarities to the chinquapin and sweet chestnut trees. However, horse chestnut seed casings usually have harder and fewer spikes compared to edible chestnuts. The seeds are also usually larger and rounder and with only one or two ‘conkers’ encased inside. They have a distinctive beige ‘eye’ on one side, which is why horse chestnut trees are often known as buckeyes, due to their similarity to deer eyes.

Where does Horse Chestnut grow?

Horse chestnuts were originally native to small pockets of Balkan forest within southeast Europe. Their showy flowers, distinctive leaves, and seed pods made them a popular choice in gardens and parks, and they have since spread across Europe. They can also be found within Canada and the US too.

Horse chestnut tree | Photo by AnRo0002 on Wikimedia Commons


A tree that is hugely valued for its unique characteristics and ornamental look, the horse chestnut also has great value to pollinators too. It’s an impressive species that should be protected and valued for its social and ecological importance.

Featured Image: Horsechestnut seeds, seed casings, and leaves. Photo by Solipsist on Wikimedia Commons

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